Lightning arrester spark gap



Dec. 1, 1964 Filed March 10, 1961 INVENTORS. flaw/m? 4. 5mm? fikza JSam/.47;

2mm VFW United States Patent 3,159,765 LHGHTNENG ARRESTER SPARK GAP Fred.l. Schuitz, Nilwaukce, and Edward lb. Sankey, Oat: Creek, Wis assiguorsto McGraw-Edison Company, Milwaukee, Wis, a corporation of DelawareFiicd Mar. 10, 196i, Ser. No. 94,812 7 Claims. (Cl. 315-65) Thisinvention relates to lightning arrestors generally and more particularlyto the spark gap component of lightning arresters.

Valve type lightning arresters in general comprise a series gap whichnormally electrically isolates the device from the line but which sparksover when a suiiiciently high voltage is impressed across the gap, and avalve element in series with the gap. The most commonly utilized valveelement is a negative resistance element which evinces a high apparentresistance at low voltages but a low apparent resistance upon relativelyhigh current flow therethru. The function of the valve element is toprovide a path to ground during surge voltages and to limit the flow offollow current, subsequent to the surge discharge, to a value that theseries gap can interrupt.

in recent years great advances have been made in lowering the IR dropacross the valve element. While this is a particularly advantageoussituation during surge discharge it also serves to increase themagnitude of allowable follow currents. Consequently more and moredilficulty has been experienced in the design of Spark gaps which willinterrupt the increased follow currents. It has been found that simplespark gaps will no longer perform the required current interruption.

Various means have been designed to supplement the interrupting abilityof a simple gap. These means serve to constrict, elongate, and split thearc between the spark gap terminals. By and large the above effects onthe are are initiated by magnetic means, i.e., the coil or permanentmagnet utilized serves to force are motion in a predetermined manner.

In particular, when coils are utilized to obtain magnetic flux in orderto force are motion, the coil itself is subjected to high overvoltagesdue to the surge current. Quite frequently these high overvoltages causeirreparable harm to the coil thereby rendering the arrester completelyinoperable and/ or possibly causing permanent line lockout.

We have designed a spark gap structure which will not be subject to thedamaging effects of high overvoltages.

It is therefore an object of this invention to provide an improvedlightning arrester having means for protecting the arc motion initiatingdevice from damaging overvoltages. I

Another object of this invention is to provide a simple and inexpensivemeans of protecting the arc motion initiating device which involves nomoving parts.

Another object of this invention is to provide a spark gap structurewhich is compact in design.

A further object of this invention is to provide a spark gap structurewith improved current interrupting ability and with improvedself-protective characteristics.

Other objects and advantages of our invention will be apparent from thefollowing description of the preferred embodiment of the invention takenin connection with the accompanying drawings in which:

FIG. 1 is a schematic diagram of a portion of the invention;

FIG. 2 is an elevation view, partially in section, of a valve typelightning arrester embodying a spark gap arrangement in accordance withthe invention;

P16. 3 is a cutaway plan view of the invention;

FIG. 4 is a view in elevation of the complete assembly of FIG. 3; and

same Patented Dec. 1, 1964 FIG. 5 is a partially cutaway view inelevation of a slightly modified device.

Referring now to the schematic diagram of FIG. 1, 1i) and 11 are spacedapart electrodes. The spaced apart electrodes 10 and 11 are so shapedthat they first converge relative to one another and then diverge. Theleast distance between the two electrodes defines a spark gap 12. Theelectrode 10 is connected directly to the line (L) while the electrode11 is connected to ground (G) thru a valve element 9 which may have anegative resistance characteristic.

An electrical coil 13 or similar are moving means is connected to theline electrode 10 as shown in FIG. 1. In series with the coil 13 is anauxiliary electrode 14 which has a portion 14 which extends between theelectrodes 10 and 11. Since the end of the electrode portion 14 is notin contact with either of the electrodes 1%) and 11 two air gaps 15 and16 exist, respectively, between the electrode portion 14 and thedivergent surface of electrode 16 and between the electrode portion 14and the divergent surface of electrode 11. It can therefore be seen thatthe coil 13, electrode i4, and gap 16 constitute a current path which isin parallel with the basic path between electrodes 19 and 11.

During a surge such as a lightning stroke the spark gap 12 sparks overand a path to ground is created. Subsequently 60 cycle follow currentflows thru the electrode 10, gap 12, electrode 11 and to ground. Due tothe divergent relation of the electrodes 16 and 11 and as a result ofthe magnetic interaction of the arc and current in the electrodes 16 and11, the arc is moved outwardly between the electrodes 10 and 11 therebyelongating same. When the follow current are is moved a su'tiicientdistance outwardly between the electrodes 10 and 11 it will transfer tothe auxiliary electrode portion 14, i.e., arcs will exist betweenelectrode lit and portion 14 and between portion 14 and electrode 11.Upon transfer of the arc to the electrode 14 (portion 14') followcurrent is transferred thru the coil 13 causing a great increase in theflux density and force on the arc. Since the coil 13 is now in thecircuit a greatly increased magnetic flux density is created which canbe used to constrict, split, elongate or otherwise manipulate the arc inorder to expedite its interruption.

it is apparent from the above description that the coil 13 is protectedfrom high overvoltages since it does not appear in the circuit until thesurge has passed and 60 cycle follow current is flowing. This then isone aspect of the invention.

In FIGURE 3 an operative form of the invention is shown which isbasically similar to FIGURE 1. The device of FIGURE 3 includes arelatively fiat insulating housing 17 having a plurality of inwardlyextending finger projections 18. The inwardly extending fingers 18 maybe a portion of the insulating housing 17 or they may be metallic orotherwise conducting portions. The different construction of the fingersIt) involves somewhat difierent modes of operation which will bediscussed subsequently. An inwardly extending line 1h is connected tothe electrode 1i and a line to ground 2b is connected to the electrode11'. The electrode 11 is generally V-shaped and first converges withrespect to the electrode 10 and then diverges with respect theretofinally culminating in an area adjacent the periphery of the housing 17.The electrode 14 extends inwardly from the periphery of the housing 17toward the center thereof and culminates in a portion 14 which isjuxtaposed between portions of the electrodes iii and 11. As before acoil or similar means 13 is positioned in a circuit parallel with thegap 12 and in series with the auxiliary electrode 14.

The gaps l5 and 12 are so co-ordinated that in operation during a surge,only gap 12 sparks over between the electrodes Hi and 11. Subsequently,60 cycle follow current flows and due to the configuration of the electrodes and as a result of the magnetic interaction of the arc and thecurrent in the electrodes the arc is moved outwardly between theelectrodes it? and 13 until it con tacts the portion id of the auxiliaryelectrode 14, at which time the follow current are exists betweenelectrode 1i) and portion 14 and portion 14 and electrode Ill. It willbe noted that the original arc path across the gap 12 is generallynormal to the direction of the current path in each of the electrodeslit) and 11. It is the inherent magnetic effect of the current flowitself which aids in moving the arc outwardly along the electrodes. Whenthe electrode 14 becomes a part of the arcing circuit the arc volt-agedrop in gap l5'is of such a magnitude as to cause current to transferthrough the path including the coil 13. Therefore the coil 13 isinserted into the circuit, the are 15 becomes unstable andself-extinguished, and a current path exists through line 19, electrode14, electrode f1 and through line 2-9 ultimately to ground.

Since the coil 13 is now operating on the are it (the arc) may beelongated and deformed to the extent that the termini thereof are movedalong the surface of the electrodes 14 and if. toward the periphery ofthe housing 1.7. As the arc becomes elongated it conforms to the innerperiphery of the housing 17 and is further elongated in that it extendsup one side and down the other side of the inwardly extending insulatingfinger projections 18. in this manner extinction of the arc is greatlyfacilitated.

If the finger projections 13 are constructed of conducting material suchas metal they may be properly termed finger electrodes. In this case thearc, instead of being elonagted by extending it around the fingerprojections, is broken up into a plurality of smaller arcs which existbetween the adjacent metallic (conducting) fingers. In both cases(insulating or conducting fingers) the coil 13 serves to force the areinto the vicinity of the finger projections so that are extinction isgreatly facilitated.

We have found that the above described means of protecting the coil isexceedingly practical in that the coil may be switched into the powerfollow current circuit within 490-1200 microseconds depending upon thegap spacings and the particular configuration of the electrodes. Hencethe coil is protected against surges and yet there is no appreciabletime delay before the coil begins to act on the arc to aid in theextinction of same.

In FIG. 4 one means of providing the above described structure isillustrated. This involves a split housing 17 which is made up ofportions 24 and 25 which are afixed together to encase the electrode andcoil assemblies.

In FIG. 2 the spark gap structure is shown in conjunction with alightning arrester having a skirted housing 21, a valve element 9' andan insulating cap 22. As can be seen, the spark gap structure 2131 ispositioned atop the valve element 9' in series relation tl'ierewith andin series with the incoming line 1% though many other arrangements areequally possible. The basic spark gap unit described herein may beconnected serially to similar units to form higher voltage assembliesbut this or other modifications of the basic invention are not shown ordiscussed as the basic principle involved in the same for thesemodifications. The spark gap assembly of the invention may be utilizedwith a variety of lightning arrester housing structures and theparticular structure shown and described herein is by way of exampleonly of one such structure.

In FIG. 5 a partially cutaway portion of a slightly modified arrangementis shown. in this modification the faces of the mating portions 24', 25'(which serve to enclose the electrodes, coil etc.) of the insulatedhousing 17' are beveled toward one another so that as the arc is movedfrom portion A of the assembly to portion B it (the arc) comes more incontact with the mating insulating surfaces. This causes the arc to becooled and constricted by the narrowing insulating surfaces therebyfacilitating extinction of same. Finger projections similar to thosepreviously discussed may or may not be utilized in this embodimentdepending on the de sired operating characteristics of the assembly butthese are not shown in order to shorten the disclosure and to facilitatethe understanding thereof.

While only a few embodiments of the invention have been shown anddescribed, it will be obvious to those skilled in the art that variouschanges and modifications can be made therefrom without departing fromthe invention and, therefore it is intended for the appended claims tocover all such changes and modifications as fall within the true spiritand scope of the invention.

We therefore claim:

1. A lightning arrester spark gap assembly comprising in combination, apair of spaced apart divergent electrodes, said electrodes definingtherebetween at their point of greatest confluence a spark gap, one ofsaid pair of electrodes being connected to a source of higher potentialthan the other of said electrodes, are moving means connected to saidsource of higher potential, an auxiliary electrode in series with saidare moving means and having a portion thereof spacedly juxtaposedbetween portions of said pair of electrodes, said one of said pair ofelectrodes and said auxiliary electrode and said other of said pair ofelectrodes and said auxiliary electrode defining respectivelytherebetween spark gaps; said are moving means, said auxiliaryelectrode, the spark gap between said auxiliary electrode and said otherof said pair of electrodes and said other of said pair of electrodesconjointly defining a follow current path in parallel with said sparkgap defined by said pair of electrodes, and means in the vicinity ofsaid pair of electrodes for facilitating extinction of the followcurrent are, whereby said are moving means is inserted into the powerfollow current circuit subsequent to the surge to thereby protect saidare moving means against the effects of the surge and to allow said aremoving means to force the follow current are into contact with said areextinction facilitating means.

2. A lightning arrester spark gap construction comprising incombination, a first electrode, a second electrode spaced apart fromsaid first electrode, said first electrode being connected to a sourceof higher potential than said second electrode, said electrodes beingconvergent and then divergent with respect to one another and definingtherebetween in the vicinity of the point of their greatest confluence amain spark gap which is capable of breaking down on surges, coil meansin electrical connection with said source of higher potential, auxiliaryelectrode means in series with said coil means, said auxiliary electrodemeans having a portion thereof disposed between said first and secondelectrodes, said auxiliary electrode and said second electrode definingtherebetween a spark gap, said first electrode, said main spark gap andsaid second electrode constituting a surge current path; said coil, saidauxiliary electrode, said gap between said auxiliary electrode and saidsecond electrode, and said second electrode constituting a 60 cyclefollow current path; and means associated with said electrodes forfacilitating extinction of the follow current arc, whereby subsequent toa surge the arc existing between said first and second electrodes movesalong the divergent portions of said first and second electrodes to saidauxiliary electrode to insert said coil and said auxiliary electrodeinto the follow current circuit thereby providing a sufiicient value offlux to force the follow current are into contact with said areextinction facilitating means.

3. A lightning arrester spark gap assembly comprising a housing, a firstelectrode, a second electrode spaced a, art from said first electrode,said first and second electrodes defining therebetween a surge gap andfurther characterized by having portions thereof which are divergent toone another, coil means for moving the arc in said surge gap, auxiliaryelectrode means in series with said coil means, said auxiliary electrodemeans having a portion thereof situated between said first and secondelectrode means, said auxiliary electrode means and said secondelectrode defining therebetween a follow current gap, said first andsecond electrodes and the surge gap therebetween defining a surge path;said coil, said auxiliary electrode and said second electrode and thefollow current gap therebetween defining a power follow current path,and are extinction means in proximity to said electrodes, whereby thearc instituted between said first and second electrodes during surgessubsequently moves along said divergent electrode portions and transfersto said auxiliary and second electrodes whereupon said coil means isinserted into the circuit to force said are into contact with said arcextinction means.

4. A lightning arrester spark gap assembly comprising an insulatinghousing having a tortuous inner periphery, a first electrode, a secondelectrode spaced apart from said first electrode, said first and secondelectrodes defining therebetween a surge gap and further characterizedby having portions thereof which are divergent to one another, coilmeans for moving the arc in said surge gap, auxiliary electrode means inseries with said coil means, said auxiliary electrode means having aportion thereof situated between said first and second electrode means,said auxiliary electrode means and said second electrode definingtherebetween a follow current gap, said first and second electrodes andthe surge gap therebetween defining a surge path; said coil, saidauxiliary electrode and said second electrode and the follow current gaptherebetween defining a follow current path, whereby the arc institutedbetween said first and second electrodes during surges subsequentlymoves along said divergent portions of said electrodes and transfers tosaid auxiliary electrode whereupon said coil means is inserted into thecircuit and by virtue of the increased magnetic fiux density the arc isforced around the tortuous inner periphery of said housing to elongateit and to facilitate extinction of same.

5. A lightning arrester spark gap assembly comprising an insulatinghousing, a first electrode, a second electrode spaced apart from saidfirst electrode, said first and second electrodes defining therebetweena surge gap and further characterized by having portions thereof whichare divergent to one another, coil means for moving the arc in saidsurge gap, auxiliary electrode means in series with said coil means,said auxiliary electrode means having a portion thereof situated betweensaid first and second electrode means, said auxiliary electrode meansand said second electrode defining therebetween a follow current gap,said first and second electrodes and the surge gap therebetween defininga surge path; said coil, said auxiliary electrode and said secondelectrode and the follow current gap therebetween defining a followcurrent path,

and a plurality of inwardly projecting finger electrodes arranged aroundthe inner periphery of said housing, whereby the arc instituted betweensaid first and second electrodes during surges subsequently moves alongsaid divergent portions of said electrodes and transfers to saidauxiliary electrode whereupon said coil means is inserted into thecircuit and by virtue of the increased magnetic flux density the are isforced into contact with said finger electrodes to split it into aplurality of smaller arclets to thereby facilitate extinction of same.

a. A lightning arrester spark gap assembly comprising an insulatinghousing having convergent insulating surfaces, a first electrode, asecond electrode spaced apart from said first electrode, said first andsecond electrodes defining therebetwecn a surge gap and furthercharacterized by having portions thereof which are divergent to oneanother, coil means for moving the arc in said surge gap, auxiliaryelectrode means in series with said coil ieans, said auxiliary electrodemeans having a portion thereof situated between said first and secondelectrode means, said auxiliary electrode means and said secondelectrode defining therebetween a follow current gap, said first andsecond electrodes and the surge gap therebetween defining a surge path;said coil, said auxiliary electrode and said second electrode and thefollow current gap therebetween defining a follow current path, wherebythe arc instituted between said first and second electrodes duringsurges subsequently moves along said divergent portions of saidelectrodes and transfers to said auxiliary electrode whereupon said coilmeans is inserted into the circuit and by virtue of the increasedmagnetic flux density the arc is forced into contact with saidinsulating surfaces of said housing to constrict and to facilitate theextinction of said arc.

7. A lightning arrester spark gap construction comprising incombination, a pair of spaced apart electrodes defining therebetween afirst spark gap surge path, are moving means, auxiliary electrode meansin series with said are moving means and having a portion thereof inspaced proximity to at least one of said pair of electrodes so as todefine a second spark gap therebetween, said are moving means, saidauxiliary electrode, means said second spark gap and said one of saidpair of electrodes defining a follow current path in shunt with saidfirst spark gap, and means in the vicinity of said second spark gap forfacilitating extinction of the follow current are, said follow currentpath being open and said second spark gap means not breaking down untilsubsequent to the surge in rder to protect said are moving means fromthe surge and said are moving means acting upon said follow current arcand moving it into the vicinity of said are extinction facilitatingmeans.

References Cited in the file of this patent UNITED STATES PATENTS

1. A LIGHTNING ARRESTER SPARK GAP ASSEMBLY COMPRISING IN COMBINATION, APAIR OF SPACED APART DIVERGENT ELECTRODES, SAID ELECTRODES DEFININGTHEREBETWEEN AT THEIR POINT OF GREATEST CONFLUENCE A SPARK GAP, ONE OFSAID PAIR OF ELECTRODES BEING CONNECTED TO A SOURCE OF HIGHER POTENTIALTHAN THE OTHER OF SAID ELECTRODES, ARC MOVING MEANS CONNECTED TO SAIDSOURCE OF HIGHER POTENTIAL, AN AUXILIARY ELECTRODE IN SERIES WITH SAIDARC MOVING MEANS AND HAVING A PORTION THEREOF SPACEDLY JUXTAPOSEDBETWEEN PORTIONS OF SAID PAIR OF ELECTRODES, SAID ONE OF SAID PAIR OFELECTRODES AND SAID AUXILIARY ELECTRODE AND SAID OTHER OF SAID PAIR OFELECTRODES AND SAID AUXILIARY ELECTRODE DEFINING RESPECTIVELYTHEREBETWEEN SPARK GAPS; SAID ARC MOVING MEANS, SAID AUXILIARYELECTRODE, THE SPARK GAP BETWEEN SAID AUXILIARY ELECTRODE AND SAID OTHEROF SAID PAIR OF ELECTRODES AND SAID OTHER OF SAID PAIR OF ELECTRODESCONJOINTLY DEFINING A FOLLOW CURRENT PATH IN PARALLEL WITH SAID SPARKGAP DEFINED BY SAID PAIR OF ELECTRODES, AND MEANS IN THE VICINITY OFSAID PAIR OF ELECTRODES FOR FACILITATING EXTINCTION OF THE FOLLOWCURRENT ARC, WHEREBY SAID ARC MOVING MEANS IS INSERTED INTO THE POWERFOLLOW CURRENT CIRCUIT SUBSEQUENT TO THE SURGE TO THEREBY PROTECT SAIDARC MOVING MEANS AGAINST THE EFFECTS OF THE SURGE AND TO ALLOW SAID ARCMOVING MEANS TO FORCE THE FOLLOW CURRENT ARC INTO CONTACT WITH SAID ARCEXTINCTION FACILITATING MEANS.